Bearing condition monitor for a vehicle, such as a truck or a trailer

ABSTRACT

A system for monitoring bearing health of a wheel of a vehicle, such as a trailer, is provided. The system is configured to monitor at least one characteristic relating to the wheel bearings, such as a temperature, vibrations, and/or proximity. The monitoring system may be configured to monitor more than one of these characteristics (i.e., temperature, vibration and proximity) or even all three. The system is incorporated into a wheel speed sensor. The system may be incorporated in an anti-lock brake system (ABS) or electro-pneumatic brake system (EBS). Regardless of which characteristic is actually monitored by the system and whether the system is employed with an ABS or EBS, the bearing monitoring system provides that one or more bearings of a vehicle can be continuously and automatically monitored in the field.

[0001] This application claims the priority of provisional applicationSer. No. 60/171,741, filed on Dec. 22, 1999, and entitled “SensingSystem For a Trailer Wheel”.

BACKGROUND OF THE INVENTION

[0002] This invention is generally directed to a bearing monitoringsystem for a vehicle, such as a trailer or a truck. The bearingmonitoring system is provided in combination with a wheel speed sensor.

[0003] Wheel bearing failure is a serious occurrence for trucks,trailers and for all wheeled vehicles. A seized bearing can result inthe complete loss of a wheel, including both rims and tires. After thewheel separates from the vehicle, the potential for catastrophic damageis present as the wheel may strike other vehicles or stationery objects.Loss of control of the vehicle itself may also result.

[0004] On trailers, both oil and grease lubrication systems are used andcorrect lubrication plays an important role in continued safe bearingoperation. For both oil and grease, the lubrication system can fail. Foroil, a seal failure can result in significant oil loss and eventualdisruption of the lubricating oil film. For grease, the bearing may nothave been packed properly to begin with.

[0005] An advantage with grease is that, even after seal failure, amajor leakage still does not occur. In contrast, with oil, significantleakage occurs. This cause loss of lubricant and the oil may contaminateother components. Contaminated brake linings in particular can result inpoor and/or unbalanced braking.

[0006] Grease, however, has the disadvantage that the grease cannotreally be inspected without removing the hubcap, and ideally the entirehub assembly. In contrast, with oil, a sight glass in the hubcap allowsconfirmation that oil is present to the correct level.

[0007] It is desirable to have some means of monitoring the integrity ofthe bearing system, especially for grease applications. This enables themonitoring the presence of lubricant directly. Alternatively, themonitoring means can monitor bearing behavior and provide a warning tothe operator if the bearings showed signs of operating without theappropriate lubrication, or if this is not possible, at least provideprior warning of impending failure.

[0008] If the bearing is starved of lubrication, rapid wear occurs whicheventually results in bearing failure. Also, bearing temperaturesincrease. Characteristic vibrations tend to occur as oil films breakdown and metal to metal contact occurs.

[0009] These effects can potentially be used to provide warning beforeactual failure.

[0010] In some cases, warning can be provided even before appreciablewear has occurred. By restoring proper lubrication, the bearing systemcan be put back into service without component replacement. In othercases, however, the warning will be in advance of actual failure butwould still require component replacement.

[0011] Either is a significant advantage for trucks and trailers.Avoidance of in service bearing failure, even if component replacementis required, is a great advantage. Not only is safety increased butfleets can potentially move to a maintenance on-demand system. Withcurrent practice, wheel hubs and bearings are normally serviced after agiven mileage or service time. Wheel ends with lubrication and bearingssystems intact and capable of many more miles are dismantled justbecause of the maintenance schedule. Extending maintenance intervalsresults in a direct economic advantage. Extending maintenance intervalsalso has secondary benefits in that for any maintenance operation, thereis always the chance that something gets broken or is reassembledincorrectly. Quality control of field operations can rarely be aseffective as the quality systems in place at vehicle assembly plants.

[0012] Providing the monitoring function economically is important toachieve mainstream acceptance in the trucking industry. Wiring harnesseswhich connect to temperature, acceleration and/or proximity sensors areexpensive. Also, electronics to process the information and providewarning for the driver and/or maintenance personnel adds additionalexpense.

[0013] The present invention provides a bearing monitoring system for avehicle, such as a trailer or a truck. Features and advantages of thepresent invention will become apparent upon a reading of thespecification in combination with a study of the drawings.

OBJECTS AND SUMMARY OF THE INVENTION

[0014] A general object of the present invention is to provide a bearingmonitoring system for a vehicle, such as a trailer or a truck.

[0015] An object of the present invention is to provide a bearingmonitoring system for a vehicle, such as a trailer or a truck which isprovided in combination with a wheel speed sensor.

[0016] Briefly, and in accordance with at least one of the foregoingobjects, an embodiment of the present invention provides a bearingmonitoring system for monitoring a bearing of a wheel of a vehicle, suchas a truck or a trailer. The bearing monitoring system is configured tomonitor at least one characteristic relating to the wheel bearings, suchas a temperature generally proximate the bearings, vibrations of one ormore elements of the wheel mounting apparatus, and/or the proximity of arotating element of the wheel. The monitoring system may be configuredto monitor more than one of these characteristics (i.e., temperature,vibration and proximity) or even all three. The bearing monitoringsystem is incorporated into a wheel speed sensor. The bearing monitoringsystem may be incorporated in an anti-lock brake system (ABS) orelectro-pneumatic brake system (EBS). Regardless of which characteristicis actually monitored by the system and whether the system is employedwith an ABS or EBS, the bearing monitoring system provides that one ormore bearings of a vehicle can be continuously and automaticallymonitored in the field.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The organization and manner of the structure and operation of theinvention, together with further objects and advantages thereof, maybest be understood by reference to the following description, taken inconnection with the accompanying drawings, wherein like referencenumerals identify like elements in which:

[0018]FIG. 1 is a block diagram of a prior art anti-lock brake system;

[0019]FIG. 2 is a side elevational view of a trailer and a partial sideelevational view of a tractor on which the ABS or EBS which incorporatesthe features of the present invention is used;

[0020]FIG. 3 is a block diagram of an anti-lock brake system (ABS) or anelectro-pneumatic brake system (EBS) which incorporates the features ofthe present invention;

[0021]FIG. 4 is a partial cross-sectional view of a wheel mountingapparatus which includes a wheel speed sensor which incorporates thefeatures of the invention;

[0022]FIG. 5 is an enlarged section of FIG. 4;

[0023]FIG. 6 is a perspective view of a portion of the wheel speedsensor;

[0024]FIG. 7 is an enhancement circuit which is used in the presentinvention;

[0025]FIG. 8 is a partial cross-sectional view of an alternate wheelmounting apparatus which includes a wheel speed sensor whichincorporates the features of the invention;

[0026]FIG. 9 is an electronic schematic of an implementation of thepresent invention; and

[0027]FIG. 10 is a schematic of the wheel speed sensor and ABS.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

[0028] While the invention may be susceptible to embodiment in differentforms, there is shown in the drawings, and herein will be described indetail, a specific embodiment with the understanding that the presentdisclosure is to be considered an exemplification of the principles ofthe invention, and is not intended to limit the invention to that asillustrated and described herein.

[0029] The present invention provides a bearing monitoring system formonitoring the health of a bearing 34, 36 of a wheel of a vehicle 26,such as a truck or a trailer. The bearing monitoring system isconfigured to monitor at least one characteristic related to thebearings 34, 36, such as a temperature generally proximate the bearings34, 36, vibrations of one or more elements of the wheel mountingapparatus 24, and/or the proximity of a rotating element of the wheel.The monitoring system may be configured to monitor more than one ofthese characteristics (i.e., temperature, vibration and proximity) oreven all three. The bearing monitoring system may be incorporated in ananti-lock brake system (ABS) or electro-pneumatic brake system (EBS).Regardless of which characteristic is actually monitored by the bearingmonitoring system and whether the bearing monitoring system is employedwith an ABS or EBS, the bearing monitoring system provides that one ormore bearings 34, 36 of the vehicle 26 can be continuously andautomatically monitored in the field. The bearing monitoring system ofthe present invention is provided in a wheel speed sensor 20.

[0030] The specifics of the physical parameters of the sensor 20 isdescribed in copending patent application Serial No. (Not Yet Assigned),filed on Dec. 21, 2000, entitled “Axle End Wheel Sensor For A Truck Or ATrailer”. The specifics of the wheel speed and direction sensing by thesensor 20 is described in co-pending patent application Ser. No. (NotYet Assigned), filed on Dec. 21, 2000, entitled “Anti-Lock Brake SystemFor A Truck Or A Trailer, Including Back-up Alarm And/or Lamps”. Each ofthese patent applications claim the priority of provisional applicationSer. No. 60/171,741 upon which the present application claims priority.Each disclosure of these patent applications are commonly owned by theassignee herein and are incorporated herein in their entirety. Thesensor 20 is provided in an apparatus 24 for mounting a wheel on thetrailer 26.

[0031] A block diagram an anti-lock brake system (ABS) or anelectro-pneumatic brake system (EBS) for a trailer 26 in accordance withthe present invention is shown in FIG. 3. The present invention providesa wheel sensing arrangement which provides information to a controller,such as an electronic control module (ECM). Power (12 Volts) to the ECMis supplied from pin 7 of the J560 connector 18 between the tractor 16and the trailer 26. The ECM controls a pneumatic control module (PCM)which controls the brake mechanism on the trailer 26. The ECM alsocontrols the function of a system, such as a warning system in the cabof the tractor 16 which is used to alert the operator, as describedherein. The ECM of the ABS or EBS signals the PCM of the ABS or EBS tomodify air pressure level at the brake chambers. The braking level iscontrolled so that the wheels continue to rotate, or at least rotatemost of the time, even during heavy braking. The overall process isdescribed in detail in numerous patents and in the pending U.S. patentapplication Ser. No. 09/306,921, which is commonly owned by the assigneeherein and which is incorporated by reference.

[0032] The wheel mounting apparatus 24 generally includes the axle 22, awheel hub assembly 28 and a brake mechanism. The brake mechanism is ofknown construction and as such is not described in detail herein.

[0033] The axle 22 is fixedly mounted on the body of the trailer 26 bysuitable means and is formed from a hollow tube (only one end of whichis shown in FIG. 4). The ends of the hollow axle 22 have a thread formon the exterior surface thereof. The inner surface of each end of theaxle 22 has a portion 30 which has an increased inner diameter relativeto an inner diameter of a central portion of the axle 22. The axle 22 isformed from a suitable strong rigid material.

[0034] The wheel hub assembly 28 is mounted on the end of the axle 22and generally surrounds the axle 22. The wheel hub assembly 28 includesa wheel hub 32, a plurality of inner bearings 34, a plurality of outerbearings 36, and a metal hub cap 38. The wheel hub 32 is attached to thebrake drum by suitable known means, such as bolts.

[0035] The inner and outer bearings 34, 36 are mounted between the wheelhub 32 and the axle 22 by respective bearing cups 40 and bearing cones42 and allow for rotation between the fixed axle 22 and the rotatingwheel hub assembly 28 and the brake mechanism. The outer bearings 36 aremounted in the portion 33 such that the bearing cups 40 abut against ashoulder formed by the portion 33. This precisely mounts the outerbearings 36 on the axle 22. The inner and outer bearings 34, 36 aremounted at locations which are spaced apart from each other along thelength of the axle 22 such that a cavity 44 is provided between thewheel hub 32, the axle 22 and the bearings 34, 36. A bath of oil orsemi-fluid synthetic grease is contained within the cavity 44. Thebearings 34, 36 are lubricated by the bath of oil or semi-fluidsynthetic grease contained therewithin.

[0036] The hub cap 38 surrounds the end of the axle 22 and prevents theoil or grease from leaking out of the end of the wheel hub assembly 28.The hub cap 38 includes a circular outer end wall 46, a first side wall48, a second side wall 50, a third side wall 52 and an inner end wall54. The walls 46, 48, 50, 52, 54 are integrally formed with each other.The first side wall 48 is generally perpendicular to the outer end wall46 and has a first end connected to the outer end wall 46 and tapersfrom its first end to its second, larger end. The second side wall 50has a first end connected to the second end of the first side wall 48and tapers from its first end to its second, larger end. The third sidewall 52 has a first end connected to the second end of the second sidewall 50 and tapers from its first end to its second, larger end. Theinner end wall 54 is annular and is generally perpendicular to the thirdside wall 52 and has a first end connected thereto and extends outwardlytherefrom. The inner end wall 54 is parallel to the outer end wall 46. Aplurality of apertures are provided through the inner end wall 54through which the hub cap 38 is attached to the end of the wheel hub 32by suitable means, such as bolts 56.

[0037] The third side wall 52 has an end portion 55 which extends pastthe inner end wall 54. When the hub cap 38 is mounted on the wheel hub32, the end portion 55 seats within the portion 33 of the wheel hub 32and abuts against the cones 40 of the outer bearings 36. This locatesthe hub cap 38 precisely on the wheel hub 32 and on the axle 22.

[0038] A washer 58 is mounted on the threaded end of the axle 22 andbears against the bearing cones 42 of the outer bearings 36. An inneradjusting nut is 60 threaded onto the threaded end of the axle 22 andbears against the washer 58. The adjusting nut 60 is locked onto theaxle 22 by threading an outer jam nut 62 on the threaded end of the axle22. The adjusting nut 60 is used to properly position the outer bearings36. The washer 58, the inner adjusting nut 60 and the outer jam nut 62are proximate to the third side wall 52 of the hub cap 38. The washer58, the inner adjusting nut 60 and the outer jam nut 62 do notcompletely fill the space between the axle 22 and the hub cap 38 suchthat a space is formed therebetween. It is to be understood that othercomponents can be threaded on the end of the axle 22 to properlyposition the outer bearings 36.

[0039] A freeze plug 64 sits within and fills the end portion 30 of theaxle 22. The freeze plug 64 has a circular central portion 66 and anannular skirt 68 which depends therefrom. The skirt 68 tightly engageswith the inner surface of the end portion 30 of the axle 22. A centralaperture 70 and a second aperture (not shown) therethrough which isoffset from the central aperture 70 are provided through the centralportion 66 of the freeze plug 64. A grommet (not shown) is providedwithin the second aperture. The freeze plug 64 prevents oil or greasefrom entering into the axle 22 and prevents debris from going fromwithin the axle 22 outwardly therefrom.

[0040] The sensor 20 includes a sensor member 72 which is mounted in theend of the axle 22 and is spaced from the freeze plug 64. The sensormember 72 includes a plastic body 76 which extends partially into theend of the axle 22 and extends outwardly therefrom, and a plastic cover78 which covers the section of the body 76 which extends outwardly fromthe end of the axle 22. The cover 78 is suitably secured to the body 76.A recess is formed between the body 76 and the cover 78. A centralaperture 80 is provided through the body 76 and the cover 78 and alignswith the central aperture 70 through the freeze plug 64. A plurality ofL-shaped vents 81 are provided through the periphery of body 76 toprovide an air passageway from the space between the freeze plug 64 andthe body 76 and the space between the sensor member 72 and the hub cap38.

[0041] The body 76 of the sensor member 72 is fastened to the axle 22 bya bolt 82 which is mounted in the central aperture 80 through the body76. The bolt 82 threads with the central aperture 70 through the freezeplug 64. The thread form in the freeze plug 64 may be pre-tapped or maybe generated using a thread forming bolt.

[0042] The central aperture 80 in the body 76 allows for the possibilityof an air passage through the body 76 if a hollow bolt 82 is utilized asshown. This allows for the incorporation of a central tire inflation(CTI) in the present system. CTI systems automatically keep tiresinflated by passing air from a compressed air reservoir mounted on thetrailer 26 to the tires. One possible implementation of a CTI systemwith the present invention passes air through a tube in the hollow axle22, then through a swivel connection with a rotating seal to airfittings on the outside of the hub cap 38. The air is then piped to theinflation valves for the tires. A suitably designed hollow bolt 82allows for the air to pass from the tube in the hollow axle 22 to therotating seal in the hub cap 38. The sensor member 72 of the presentinvention allows for CTI but does not economically penalize the majorityof applications where CTI is not used.

[0043] To protect the bearings 36, 38, the entire axle end area issealed from moisture, dirt and other contaminants. Suitable venting isprovided so that the seals within the wheel mounting apparatus 24 arenot subjected to excessive pressure buildup. Depending on the wheel endconstruction, different methodologies may be used which use suitablevents in the hub cap 38, seals and/or the freeze plug 64. The sensormember 72 of the present invention is compatible with all suchapproaches. Consequently, the periphery of the body includes theL-shaped venting slots 81 such that pressure on both the front and backof the sensor member 72 remains equalized. As for a conventional wheelend construction, venting and sealing are controlled by the hub cap,freeze plug and bearing seals. It should be noted that, depending on theapplication and the method of lubrication of the bearings, all parts ofthe sensor member 72 may be subject to oil splash. The design andmaterial of the sensor member 72 of the present invention allows foroperation in this environment.

[0044] An electronic circuit assembly 84 is provided between the body 76and the cover 78 of the sensor member 72. The electronic circuitassembly 84 includes a printed circuit board 86 mounted on the body 76by suitable means such that the printed circuit board 86 is positionedbetween the body 76 and the cover 78 of the sensor member 72. Wires 90extend from the printed circuit board 86 through the grommet in thefreeze plug 64, through the hollow axle 22 to a current supplyingcontroller 92. The controller 92 is preferably the ECM of the ABS or EBSof the trailer 26. If desired, a second controller can be provided.

[0045] Wheel speed sensing elements 94, 96 are provided on the printedcircuit board 86 in the form of an application specific integratedcircuit (ASIC) 88. The preferred embodiment of the present inventionuses “active” technology.

[0046] The wheel speed sensing elements 94, 96 are preferably a pair ofhall effect semiconductor elements. The hall effect semiconductorelements 94, 96 can be soldered to the printed circuit board 86 at theoutermost end thereof and at spaced locations from each other.Preferably, however, the hall effect semiconductor elements 94, 96 arelocated on the same silicon chip. This aids in overall economy and,because of the use of standard integrated circuit fabricationtechniques, relative location can be controlled. The face of each halleffect semiconductor sensing element 94, 96 is parallel to the axis ofrotation of the axle 22. It is to be understood that conventional VRsensors can be used instead of hall effect semiconductor sensingelements 94, 96.

[0047] The second side wall 50 of the hub cap 38 is machined to providea recess in which a mounting wheel 75 is located. To secure the mountingwheel 75 to the inside of the second side wall 50, the metal second sidewall 50 is deformed. This precisely locates the mounting wheel 75 on thehub cap 38. Because the hub cap 38 is precisely mounted on the wheel hub32 and axle 22 as discussed herein, the mounting wheel 75 is preciselymounted on the wheel hub 32 and axle 22.

[0048] An exciting ring 74 is mounted on the inner surface of themounting wheel 75 and is proximate to, but spaced from the hall effectsemiconductor sensing elements 94, 96. Because the mounting wheel 75 isprecisely mounted on the wheel hub 32 and axle 22, the exciting ring 74is precisely mounted on the wheel hub 32 and axle 22. The exciting ring74 and the sensor member 20 are concentric with each other when mounted.As such, a defined radial gap is provided between the exciting ring 74and the hall effect semiconductor sensing elements 94, 96. The halleffect semiconductor sensing elements 94, 96 are mounted on the printedcircuit board 86 so as to precisely line up with the exciting ring 74when the hub cap 38 is mounted on the wheel hub 32.

[0049] Because the face of each hall effect semiconductor sensingelement 94, 96 is parallel to the axis of rotation of the axle 22, aconstant gap is maintained by the bearings 36. Axial movement of thewheel hub 32 does not have a significant effect and no gap adjustment isrequired. The gap is set by design, and gap variation is directlycontrolled by the bearings 36. The gap is dependent on the concentricityof the mounting of the exciting ring 74 within the hub cap 38.

[0050] In the preferred implementation, the exciting ring 74 is amulti-pole magnet fabricated using ferrite in a plastic matrix material.Because the exciting ring 74 is carried on the mounting wheel 75 mountedinside the hub cap 38, the magnet poles can be located precisely bothcircumferentially around the sensor member 72 and radially relative tothe sensor member 72. The gap between the exciting ring 74 and the halleffect semiconductor sensing elements 94, 96 is radial so that the gapis directly controlled by the position of the bearings 36 and is notinfluenced by axial movement of the wheel hub 32. Alternatively, astamped, toothed ring can be used as the exciting ring 74.

[0051] The hall effect semiconductor sensing elements 94, 96 are spacedapart from each by an integral number of pole pairs or teeth, dependingon the type of exciting ring 74 that is used, plus or minusapproximately ninety degrees.

[0052] To allow for overall optimization of the sensor member 72 and forABS function or EBS function, when the present invention is used in anABS or EBS as described herein, the preferred embodiment of the excitingring 74 does not conform to the present industry standard of one hundredteeth. Instead, the present invention uses twenty-five pole pairs in theexciting ring 74. These pole pairs are precisely located so that withuse of suitable electronic resolution enhancement techniques, aninformation rate equivalent to fifty pole pairs using standardtechniques is achieved.

[0053]FIG. 7 illustrates a circuit which implements this resolutionenhancement technique. Signals A and B originate from the hall effectsemiconductor sensing elements 94, 96. Signals A and B are input into anXOR gate 99. The resulting waveform is generated as output C. Othersuitable circuits can be used.

[0054] Individual active sensing elements are the preferred sensingelements for the sensing elements 94, 96 of the present invention. Thechips which implement the Hall effect function are small. Relativelocation can be tightly controlled by mounting on the same printedcircuit board. The two hall effect semiconductor elements 94, 96 can belocated on the same silicon chip. This aides overall economy and,because of the use of standard integrated circuit fabricationtechniques, relative location becomes almost a non-issue. Two integratedcircuits can be provided on the silicon chip, each having a hall effectelement thereon.

[0055] A temperature sensing element 100 is provided on the printedcircuit board 86 and may be in the form of an application specificintegrated circuit (ASIC) 102. Numerous implementations of thetemperature sensing element 100 are possible as would be understood byone of ordinary skill in the art. The temperature sensing element 100 isused to monitor the temperature of the bearings 34, 36 in the wheelmounting apparatus 24 by measuring the temperature of the components ofthe wheel mounting apparatus 24. The temperature of the bearings 34, 36will increase under operating conditions if the bearings 34, 36 areinsufficiently lubricated which occurs when insufficient oil or greaseis present in the chamber 44. The provision of the temperature sensingelement 100 in the electronic circuit assembly 84 is ideal formonitoring the bearings 34, 36 as the printed circuit board 86 is inclose proximity to the bearings 34, 36.

[0056] The details of an implementation of the sensor electronics whichare used to determine speed, direction and temperature is shown in FIG.9. One of ordinary skill in the art could form other suitableimplementations. The circuit as shown in FIG. 9 includes an integratedcircuit 104, integrated circuit 106, resistors 108, 110, 112, andcapacitors 114, 116, 118, 120.

[0057] A suitable integrated circuit 104 is an Allegro A3422LKAintegrated circuit. The two hall effect semiconductor elements 94, 96are embedded on one piece of silicon in the integrated circuit 104 suchthat the two hall effect semiconductor elements 94, 96 are spaced asuitable distance for quadrature implementation. The Vcc pin 1 ofintegrated circuit 104 is a voltage input. The DIR pin 2 of integratedcircuit 104 outputs direction information using high/low logic. The GNDpin 3 of integrated circuit 104 is connected to ground. The SPD pin 5 ofintegrated circuit 104 outputs a frequency signal proportional to wheelspeed. The SPD pin 5 of integrated circuit 104 implements the resolutionenhancement functionality shown in FIG. 7. Resistor 110 is connected topin 5. The EI pin 4 of integrated circuit 104 is connected to ground byresistor 108.

[0058] Integrated circuit 106 senses the temperature of the componentsof the wheel mounting apparatus 24 and provides a current output whichvaries with temperature. A suitable integrated circuit 106 is an ADTMP17 integrated circuit.

[0059] In operation, to determine the speed and direction of rotation ofthe wheels, the wheel hub 32, the hub cap 38, the mounting wheel 75 andthe exciting ring 74 rotate relative to the fixed axle 22 and the sensormember 72 mounted thereon. The controller 92 supplies electric currentto the sensor member 72 through connection J1-1. The sensor member 72 isa current sink. The hall effect semiconductor sensing elements 94, 96sense whether a north pole or a south pole of the exciting ring 74 ispresent.

[0060] If a multi-pole magnet is used as the exciting ring 74, if anorth pole is present, the hall effect semiconductor sensing elements94, 96 sink 14 mamps, for example, from the controller 92, and if asouth pole is present, the hall effect semiconductor sensing elements94, 96 sink 7 mamps, for example, from the controller 92. Thisinformation is conveyed to another part of the ASIC 88, to obtain asquare wave as the poles are going by. The controller 92 determines howmany times the sensor member 72 switches between 14 mamps and 7 mamps.This change happens one hundred times every revolution of the wheel. Ifa toothed wheel is used as the exciting ring 74 and a tooth is present,the hall effect semiconductor sensing elements 94, 96 sink 14 mamps, forexample, from the controller 92. On the other hand, if a space ispresent, the hall effect semiconductor sensing elements 94, 96 sink 7mamps, for example, from the controller 92. This information is conveyedto another part of the ASIC 88, to obtain a square wave as the poles aregoing by. The controller 92 determines how many times the sensor member72 switches between 14 mamps and 7 mamps. This change happens onehundred times every revolution of the tire. It is to be understood thatthe 14 mamps and 7 mamps values described herein are nominal. Thesevalues could be other nominal values, such as 12 mamps and 6 mamps, or10 mamps and 5 mamps.

[0061] The frequency of the change is proportional to the wheel speed.This information is used by the ABS or EBS to function in a like mannerto how a conventional wheel speed sensor information is used to slow thetrailer 26, if necessary.

[0062] The frequency output on the SPD pin 5 of integrated circuit 104is implemented using high/low voltage levels. As implemented in thecircuit shown in FIG. 9, this voltage signal is converted into a twolevel current signal by the presence of resistor 110. SPD pin 5 pullscurrent through resistor 110 when SPD pin 5 is low. When SPD pin 5 ishigh, current is not pulled through resistor 110. The interfaceelectronics then senses the current variation. This keeps the overallwiring interface to three leads, power, ground and direction. Currentpulses in the power lead correspond to the passage of poles as theexciting ring 74 rotates or to the passage of teeth if a toothed ring isused. The E1 signal output on pin 4 from the integrated circuit 104 isnot required in this application and is held at ground by resistor 108.The capacitors 114, 116 provide noise suppression.

[0063] The integrated circuit 104 does not output a current, such that alow is provided, on DIR pin 2 when the trailer 26 is backing up. Thecontroller 92, which is the ECM of the ABS or EBS, detects that theintegrated circuit 104 is not outputting current and determines that thetrailer 26 is backing up. Because the forward and reverse wheel speedinformation is available to the controller 92, the information can beused to provide enhanced functionality over and above that of ABS or EBSwithout the forward and reverse wheel speed information.

[0064] Current is supplied from the ECM through connection J1-1, flowsthrough integrated circuit 106 and then out to the ECM throughconnection J1-3. The ECM completes the current path to ground andmonitors this current.

[0065] The signal is shared with the reverse indication. When reverserotation occurs, the DIR output of integrated circuit 104 is pulled lowso the current from integrated circuit 104 flows to ground throughresistor 112. The current flow to the ECM (via J1-3) goes to near zero.This is interpreted by the ECM as an indication that the trailer 26 isbacking up and that the temperature indication is not available. Becausethe temperature information and the direction information are output onthe same pin (i.e. J1-3), the ECM determines what sensor, whether fromthe semi-conductor sensing elements 94, 96 or the temperature sensingelement 100, the signal is being sent from. Utilization of connectionJ1-3 for both functions is important because extra wiring andconnections are very expensive. The entire sensing system, includingwheel speed sensing, direction sensing and temperature sensing isimplemented with only three wires (i.e. J1-1, J1-2 and J1-3), therebygenerating significant cost savings. Also, by incorporating the signalprocessing and warning electronics into the ECM of the ABS, furthersavings are achieved in overall system cost.

[0066] If the bearings 34, 36 heat up to a predetermined amount, the ECMdetermines that there is a bearing problem by comparing the signalsreceived from the temperature sensing element 100 to a known value, andactivates the circuitry to alert the operator that the bearings 34, 36need to be serviced. The circuitry can light a warning light on thetrailer 26, a warning light in the cab of the tractor 16 and/or can sendthe information to a trailer tracking system.

[0067] While the practical implementation of this sensor 20 is with theABS, the sensor 20 can be used without ABS and with a current supplyingcontroller. As noted earlier many tractors have power available on Pin 7of the auxiliary connector. In all cases, on new trailers, Pin 7 isconnected to the ECM of the ABS or EBS. It should also be noted thatthis power supply, under current mandated requirements, is not requiredto be dedicated solely to the ABS function or EBS function.

[0068] An acceleration sensing element 122, such as an accelerometer, isalso provided on the printed circuit board 86 and may form part of theASIC 102 or may be a separate integrated circuit sensing element on theprinted circuit board 86. Other suitable implementations of theacceleration sensing element 122 can be implemented by one of ordinaryskill in the art. The acceleration sensing element 122 senses vibrationsof one or more elements of the wheel mounting apparatus 24 and transmitsthis information to the controller 92. The acceleration sensing element122 may be a silicon micromachined integrated circuit. Because theprinted circuit board 86 is mounted to the body 76 of the sensor 20 andthe sensor 20 is mounted to the end of the axle 22, vibrations of one ormore elements of the wheel mounting apparatus 24 with some attenuation,are transmitted to the acceleration sensing element 122. The provisionof the acceleration sensing element 122 in the electronic circuitassembly 84 is ideal for monitoring the bearings 34, 36 as the printedcircuit board 86 is in close proximity to the bearings 34, 36.

[0069] As lubrication fails or partially fails and some direct metal tometal contact occurs between the bearing 34, 36 and the cups 40 and/orcones 42, some characteristic vibrations occur. The acceleration sensingelement 122 detects these vibrations. The raw signal is sent to the ECMand the ECM processes the raw signal and extracts frequency information.The ECM compares this frequency to known frequencies to determinewhether this is an incorrect signal. If an incorrect signal isdetermined by the ECM, the ECM determines that there is a bearingproblem and activates the circuitry to alert the operator that thebearings 34, 36 need to be serviced. The circuitry can light a warninglight on the trailer 26, a warning light in the cab of the tractor 16and/or can send the information to a trailer tracking system.Alternatively, the acceleration signals from the acceleration sensingelement 122 can be processed locally in the printed circuit board 86.The ECM of the ABS is preferably used to process the raw signal, becausethe ECM is comprised of relatively inexpensive electronic hardware, andbecause the ECM also allows comparison of signals from two or all wheelson the trailer 26 as discussed herein.

[0070] Metal proximity sensing elements 124, 126, see FIG. 10, areprovided on the printed circuit board 86 and may form part of the ASIC102. Proximity sensing element 124 senses radial proximity of the wheelmounting apparatus 24 and proximity sensing element 126 senses axialproximity of the wheel mounting apparatus 24. The proximity sensors 124,126 measure the instantaneous location of the hub cap 38 relative to theaxle 22 and, as such, can be used to determine disturbances in thecircular trajectory of the rotating components of the wheel mountingapparatus 24. These disturbances may result from poor or looseadjustment of the bearings 34, 36 or the onset of wear in the bearings34, 36. It should also be noted that axial free play results frombearing 34, 36 adjustment which is too loose and which eventually wouldresult in premature wear of the bearings 34, 36. If there are issueswith bearing wear, the wheel hub 32 will not move in a circularmovement.

[0071] If the bearings 34, 36 are loose, axial movement of the wheel hub32 occurs. It is to be understood that either of, or both of, the radialproximity sensing element 124 and the axial proximity sensing element126 may be incorporated to help determine bearing system integrity.Because the body 76 and the cover 78 of the sensor 20 are constructed ofa plastic material, the body 76 and the cover 78 do not have an effecton the metal sensing proximity sensing elements 124, 126. The provisionof the proximity sensing elements 124, 126 in the electronic circuitassembly 84 is ideal for monitoring the bearings 34, 36 as the printedcircuit board 86 is in close proximity to the bearings 34, 36.

[0072] An inwardly protruding metal extension 128 which is mounted onthe end wall 46 of the hub cap 38 and extends inwardly along the axis ofrotation of the axle 22.

[0073] The extension 128 has a first portion 130 which is mounted to theend wall 46 and a second portion 132 which extends therefrom. The firstportion 130 has a larger diameter than the second portion 132. Thesecond portion 132 of the extension 128 extends into the hollow centerof the sensor member 20 and is monitored by the radial proximity sensingelement 124 and/or an axial proximity sensing element 126. The radialproximity sensing element 124 and/or the axial proximity sensing element126 may be a suitable eddy current or other proximity sensing elementalong with the electronic circuit assembly 84. Alternatively, theextension 128 may be mounted in the body 76 of the sensor member 20 andbe wired to the electronic circuit assembly 86.

[0074] The radial sensing element 124 senses the position of the metalsecond portion 132 of the extension 128 in that it senses the distancebetween the second portion 132 and the radial sensing element 124.Therefore, the distance between the entire rotating portion of the wheelmounting apparatus 24 relative to the axle 22 is sensed. The radialsensing element 124 sends this information to the ECM. The ECM processesthis information. If the ECM detects some change in distance, the ECMactivates the circuitry to provide the warning that the bearings 34, 36need to be serviced. The circuitry can light a warning light on thetrailer 26, a warning light in the cab of the tractor 16 and/or can sendthe information to a trailer tracking system.

[0075] The axial sensing element 126 senses the position of the metalfirst portion 130 of the extension 128 in that it senses the distancebetween the first portion 130 and the axial sensing element 126.Therefore, the distance between the entire rotating portion of the wheelmounting apparatus 24 relative to the axle 22 is sensed. The axialsensing element 126 sends this information to the ECM. The ECM processesthis information. If the ECM detects some change in distance, forexample 12 thousandths, the ECM activates the circuitry to provide thewarning that the bearings 34, 36 need to be serviced. The circuitry canlight a warning light on the trailer 26, a warning light in the cab ofthe tractor 16 and/or can send the information to a trailer trackingsystem.

[0076] The signals from the proximity sensing elements 124, 126 canprocessed locally in the printed circuit board 86 or can be fed back asa raw signal to the ECM. The ECM of the ABS is preferably used toprocess the raw signal, because the ECM is comprised of relativelyinexpensive electronic hardware, and because the ECM also allowscomparison of signals from all wheels on the vehicle as discussedherein.

[0077] Preferably, a sensor member 20 is provided on each wheel of thevehicle 26. The ECM compares the two (single axle vehicle) or four(double axle vehicle) temperature, acceleration and/or proximity signalsfrom all wheels on the vehicle 26 and compares the signals with eachother in the ECM as part of an abnormality detection routine carried outin the ECM. This is particularly important with regard to temperature.The ambient temperature widely varies with the operating environment ofthe vehicle 26. By comparing the temperature signals from each wheel,the variation due to ambient temperature can be ignored. Temperaturedeviations due to bearing abnormalities can then be isolated. Thisapproach can also be important for acceleration or proximity sensing.For example, on a very smooth road surface, it is possible to be moresensitive in detection of bearing health. In contrast, on a rough roadsurface, it is necessary for the system to be more tolerant of thesevere vibrations generated by the travel over the rough road to avoidfalse warning signals. By comparing signals from all wheels of thevehicle 26, the prevailing normal condition can be determined, andtherefore abnormal deviations can be detected.

[0078] The sensor member 20 utilizes some or all of the wiring to theABS. As shown in FIG. 9, the temperature sensing element 100 shares thesame signal wire which also provides the direction signal from the speedsensing elements 92, 94. It is to be noted that temperature sensing isnot active when the trailer 26 is in reverse.

[0079] The temperature sensing element 100 and the acceleration sensingelement 122 can share the same signal wire (and may also share thesignal wire with the direction sensing elements 92, 94). Signals fromthe acceleration sensing element 122 are AC signals, while signals fromthe temperature sensing element 100 are slowly varying DC signals. Thus,the acceleration and temperature signals can share the same wire and canbe separated in the ECM.

[0080] The direction sensing elements 92, 94, the temperature sensingelement 100, the acceleration sensing element 122 and the proximitysensing elements 124, 126 can also share the same signal wire. This isdependent on the frequency ranges of the signals which are usable by theECM. It is possible to time multiplex these signals so that they areexamined in rotation by the ECM.

[0081] Another implementation (not shown) of this aspect of the presentinvention can utilize magnetic field sensors in the electronic circuitassembly 84 to track the location of the existing exciting ring 74. Afurther implementation provides an additional magnet (not shown) locatedon the mounting wheel 76.

[0082] While a preferred embodiment of the present invention is shownand described, it is envisioned that those skilled in the art may devisevarious modifications of the present invention without departing fromthe spirit and scope of the appended claims.

The invention claimed is:
 1. A bearing monitoring system for a vehiclecomprising: an axle; a wheel mounting apparatus surrounding said axle,said wheel mounting apparatus including at least one bearing; a wheelmounted on said wheel mounting apparatus; a sensor member mounted onsaid axle, said sensor member having a first sensing element mountedthereon for use in determining the temperature of said at least onebearing; and circuitry for processing information from said sensormember regarding the temperature of said at least one bearing and forperforming a function on the vehicle depending on the information sensedby said first sensing element.
 2. A bearing monitoring system as definedin claim 1 , wherein said circuitry is part of an anti-lock brake systemor an electro-pneumatic brake system for the vehicle.
 3. A bearingmonitoring system as defined in claim 1 , wherein said first sensingelement is an application specific integrated circuit.
 4. A bearingmonitoring system as defined in claim 1 , wherein said axle including atleast two wheel mounting assemblies surrounding said axle, each saidwheel mounting apparatus including at least one bearing; a wheel mountedon each said wheel mounting apparatus; a sensor member mounted on eachsaid axle and associated with each said wheel, each said sensor memberhaving a first sensing element mounted thereon for use in determiningthe temperature of said at least one bearing associated with saidrespective wheel; the information from each said sensor member beingtransmitted to said circuitry, and wherein said circuitry compares theinformation from each said sensor member prior to performing saidfunction.
 5. A bearing monitoring system as defined in claim 1 , whereintwo axles are provided, said axle including at least two wheel mountingassemblies surrounding said axle, each said wheel mounting apparatusincluding at least one bearing; a wheel mounted on each said wheelmounting apparatus; a sensor member mounted on each said axle andassociated with each said wheel, each said sensor member having a firstsensing element mounted thereon for use in determining the temperatureof said at least one bearing associated with said respective wheel; theinformation from each said sensor member being transmitted to saidcircuitry, and wherein said circuitry compares the information from eachsaid sensor member prior to performing said function.
 6. A bearingmonitoring system as defined in claim 1 , wherein said sensor memberfurther includes a second sensing element mounted thereon for use indetermining the vibrations of one or more elements of the wheel mountingapparatus; and wherein said circuitry is capable of processinginformation from said second sensing element regarding the accelerationof said wheel.
 7. A bearing monitoring system as defined in claim 6 ,further including a signal wire connected between said sensor member andsaid circuitry, wherein said information from said sensor memberregarding the temperature of said at least one bearing and saidinformation from said sensor member regarding the acceleration of saidwheel are transmitted to said circuitry on said signal wire.
 8. Abearing monitoring system as defined in claim 7 , wherein said sensormember further includes a third sensing element mounted thereon for usein determining the direction of rotation of said wheel; and wherein saidcircuitry is capable of processing information from said sensor memberregarding the direction of rotation of said wheel, said information fromsaid sensor member regarding the direction of rotation of said wheel istransmitted to said circuitry on said signal wire.
 9. A bearingmonitoring system as defined in claim 7 , further including an elementmounted on said wheel mounting apparatus; and wherein said sensor memberfurther includes a fourth sensing element mounted thereon for use indetermining the proximity of said element relative thereto by sensingthe position of said element; and wherein said circuitry is capable ofprocessing information from said fourth sensing element regarding theproximity of said element, said information from said sensor memberregarding the proximity of said element is transmitted to said circuitryon said signal wire.
 10. A bearing monitoring system as defined in claim1 , further including an element mounted on said wheel mountingapparatus; and wherein said sensor member further includes a secondsensing element mounted thereon for use in determining the radial and/oraxial proximity of said element relative thereto by sensing the radialand/or axial position of said element; wherein said circuitry is capableof processing information from said sensor member regarding the radialand/or axial position of said element.
 11. A bearing monitoring systemas defined in claim 1 , further including an element mounted on saidwheel mounting apparatus; wherein said sensor member further includes asecond sensing element mounted thereon for use in sensing vibrations ofone or more elements of the wheel mounting apparatus and a third sensingelement mounted thereon for use in determining the radial and/or axialproximity of said element relative thereto by sensing the position ofsaid element; and wherein said circuitry is capable of processinginformation from said sensor member regarding the vibrations of one ormore elements of the wheel mounting apparatus and said circuitry iscapable of processing information from said sensor member regarding theradial and/or axial position of said element.
 12. A bearing monitoringsystem as defined in claim 1 , wherein said sensor member furtherincludes a second sensing element mounted thereon for use in determiningthe speed of rotation of said wheel; and wherein said circuitry iscapable of processing information from said second sensing elementregarding the speed of said wheel.
 13. A bearing monitoring system asdefined in claim 12 , further including an exciting element mounted onsaid wheel mounting apparatus; and wherein said second sensing elementdetermines the speed of rotation of said wheel by sensing said excitingelement.
 14. A bearing monitoring system for a vehicle comprising: anaxle; a wheel mounting apparatus surrounding said axle, said wheelmounting apparatus including at least one bearing; a wheel mounted onsaid wheel mounting apparatus; a sensor member mounted on said axle,said sensor member having a first sensing element mounted thereon foruse in sensing vibrations of one or more elements of the wheel mountingapparatus; and circuitry for processing information from said sensormember regarding the vibrations of one or more elements of said wheelmounting apparatus and for performing a function on the vehicledepending on the information sensed by said first sensing element.
 15. Abearing monitoring system as defined in claim 14 , wherein saidcircuitry is part of an anti-lock brake system or an electro-pneumaticbrake system for the vehicle.
 16. A bearing monitoring system as definedin claim 14 , wherein said first sensing element is a siliconmicromachined integrated circuit.
 17. A bearing monitoring system asdefined in claim 14 , wherein said axle including at least two wheelmounting assemblies surrounding said axle, each said wheel mountingapparatus including at least one bearing; a wheel mounted on each saidwheel mounting apparatus- a sensor member mounted on each said axle andassociated with each said wheel, each said sensor member having a firstsensing element mounted thereon for use in sensing vibrations of one ormore elements of each said wheel mounting apparatus; the informationfrom each said sensor member being transmitted to said circuitry, andwherein said circuitry compares the information from each said sensormember prior to performing said function.
 18. A bearing monitoringsystem as defined in claim 14 , wherein two axles are provided, eachsaid axle including at least two wheel mounting assemblies surroundingsaid axle, each said wheel mounting apparatus including at least onebearing; a wheel mounted on each said wheel mounting apparatus; a sensormember mounted on each said axle and associated with each said wheel,each said sensor member having a first sensing element mounted thereonfor use in determining the acceleration of said wheel by sensingvibrations of one or more elements of each said wheel mountingapparatus; the information from each said sensor member beingtransmitted to said circuitry, and wherein said circuitry compares theinformation from each said sensor member prior to performing saidfunction.
 19. A bearing monitoring system as defined in claim 14 ,wherein signals accumulated by said first sensing element are processedin said sensor member.
 20. A bearing monitoring system as defined inclaim 14 , wherein signals accumulated by said first sensing element areprocessed by said circuitry.
 21. A bearing monitoring system as definedin claim 14 , wherein said sensor member further includes a secondsensing element mounted thereon for use in determining the speed ofrotation of said wheel; and wherein said circuitry is capable ofprocessing information from said sensor member regarding the speed ofsaid wheel.
 22. A bearing monitoring system as defined in claim 14 ,further including an exciting element mounted on said wheel mountingapparatus; and wherein said second sensing element determines the speedof rotation of said wheel by sensing said exciting element.
 23. Abearing monitoring system as defined in claim 14 , further including anelement mounted on said wheel mounting apparatus; and wherein saidsensor member further includes a second sensing element mounted thereonfor use in determining the radial and/or axial proximity of said elementrelative thereto by sensing the position of said element; and whereinsaid circuitry is capable of processing information from said secondsensing element regarding the radial and/or axial position of saidelement.
 24. A bearing monitoring system for a vehicle comprising: anaxle; a wheel mounting apparatus surrounding said axle, said wheelmounting apparatus including at least one bearing; a wheel mounted onsaid wheel mounting apparatus; an element mounted on said wheel mountingapparatus; a sensor member mounted on said axle, said sensor memberhaving a first sensing element mounted thereon for use in determiningthe radial and/or axial proximity of said element relative thereto bysensing the radial and/or axial position of said element relative tosaid first sensing element; and circuitry for processing informationfrom said sensor member regarding the radial and/or axial proximity ofsaid element and for performing a function on the vehicle depending onthe information sensed by said first sensing element.
 25. A bearingmonitoring system as defined in claim 24 , wherein said circuitry ispart of an anti-lock brake system or an electro-pneumatic brake systemfor the vehicle.
 26. A bearing monitoring system as defined in claim 24, wherein said wheel mounting apparatus includes a hub cap and whereinsaid element is an exciting element mounted on said hubcap whichsurrounds said sensor member.
 27. A bearing monitoring system as definedin claim 24 , wherein said wheel mounting apparatus includes a hub capand wherein said element is mounted on said hubcap and extends into saidsensor member.
 28. A bearing monitoring system as defined in claim 24 ,wherein said axle includes at least two wheel mounting assembliessurrounding said axle, each said wheel mounting apparatus including atleast one bearing; a wheel mounted on each said wheel mountingapparatus; a sensor member mounted on each said axle and associated witheach said wheel, each said sensor member having a first sensing elementmounted thereon for use in determining the radial and/or axial proximityof said element relative thereto by sensing the position of said elementassociated with said respective wheel relative to the respective firstsensing element; the information from each said sensor member beingtransmitted to said circuitry, and wherein said circuitry compares theinformation from each said sensor member prior to performing saidfunction.
 29. A bearing monitoring system as defined in claim 24 ,wherein two axles are provided, each said axle including at least twowheel mounting assemblies surrounding said axle, each said wheelmounting apparatus including at least one bearing; a wheel mounted oneach said wheel mounting apparatus; a sensor member mounted on each saidaxle and associated with each said wheel, each said sensor member havinga first sensing element mounted thereon for use in determining theradial and/or axial proximity of said element relative thereto bysensing the position of said element associated with said respectivewheel relative to the respective first sensing element; the informationfrom each said sensor member being transmitted to said circuitry, andwherein said circuitry compares the information from each said sensormember prior to performing said function.
 30. A bearing monitoringsystem as defined in claim 24 , wherein said sensor member furtherincludes a second sensing element mounted thereon for use in determiningthe speed of rotation of said wheel; and wherein said circuitry iscapable of processing information from said second sensing elementregarding the speed of said wheel.
 31. A bearing monitoring system asdefined in claim 30 , wherein said element is an exciting element; andwherein said second sensing element determines the speed of rotation ofsaid wheel by sensing said exciting element.
 32. A bearing monitoringsystem for monitoring a bearing of a wheel of a vehicle, said bearingmonitoring system comprising: brake mechanisms; circuitry in operablecommunication with said brake mechanisms; wheel speed sensors incommunication with said circuitry, said circuitry configured to operatesaid brake mechanisms depending on what is sensed by said wheel speedsensors; and at least one bearing sensor configured to monitor at leastone characteristic at least generally relating to the bearing, saidcharacteristic being at least one of a temperature proximate thebearing, vibrations of one or more elements of said wheel mountingapparatus and proximity of a rotating element of the wheel.
 33. Abearing monitoring system as defined in claim 32 , wherein saidcircuitry comprises a pneumatic control module in operable communicationwith said brake mechanisms and an electronic control module incommunication with said pneumatic control module, said at least onebearing sensor and said wheel speed sensors in communication with saidelectronic control module.
 34. A bearing monitoring system as defined inclaim 32 , further comprising an electronic circuit assembly, saidelectronic circuit assembly including said bearing sensor and at leastone of said wheel speed sensors.
 35. A bearing monitoring system asdefined in claim 32 , wherein said at least one bearing sensor comprisesa plurality of sensors including a first sensor configured to sense atemperature generally proximate the bearing, a second sensor configuredto monitor vibrations of one or more elements of said wheel mountingapparatus, and a third sensor configured to monitor the proximity of therotating element of the wheel.
 36. A bearing monitoring system asdefined in claim 35 , further comprising an electronic circuit assembly,said electronic circuit assembly including said first, second and thirdsensor and at least one of said wheel speed sensors.
 37. A bearingmonitoring system as defined in claim 32 , wherein said at least onebearing sensor is configured to monitor at least one of a radial andaxial position of the rotating member of the wheel.
 38. A bearingmonitoring system as defined in claim 32 , wherein said at least onebearing sensor comprises at least one magnetic field sensor configuredto monitor a magnetic feature relating to the bearing.
 39. A bearingmonitoring system as defined in claim 32 , wherein said bearingmonitoring system is configured to monitor a plurality of bearings, andcomprises at least one bearing sensor associated with each bearing,wherein said circuitry is configured to receive information from each ofthe bearing sensors and compare the information.